Rotation rate sensor and method for operating a rotation rate sensor

ABSTRACT

A rotation rate sensor, including at least: one oscillating mass, deflectable in a drive direction and in a detection direction oriented perpendicularly to the drive direction; one drive circuit for prompting a defined oscillatory movement of the oscillating mass in the drive direction; one circuit for detecting a measuring signal, which corresponds to the deflection of the oscillating mass in the detection direction; and one read-out circuit for reading out and pre-processing the measuring signal. The read-out circuit includes a demodulator, with which a useful signal and a quadrature signal are extractable from the measuring signal. The read-out circuit includes a sigma-delta A/D converter. An offset voltage is feedable to the sigma-delta A/D converter, which is selected in such a way that tonal artifacts in the frequency spectrum of the digitized useful signal are shifted into a frequency range outside of the bandwidths of the useful signal to be expected.

CROSS REFERENCE

The present application claims the benefit under 35 U.S.C. § 119 ofGerman Patent Application No. DE 102020203571.7 filed on Mar. 19, 2020,which is expressly incorporated herein by reference in its entirety.

FIELD

The present invention relates to a rotation rate sensor. The presentinvention also relates to a method for operating a rotation rate sensor.

BACKGROUND INFORMATION

Rotation rate sensors measure the rotation velocity of a body. Acommercially available rotation rate sensor could include the followingcomponents: an oscillating mass, which is deflectable in a drivedirection and a detection direction oriented perpendicularly to thedrive direction; a drive circuit for prompting a defined oscillatorymovement of the oscillating mass in the drive direction; a circuit fordetecting a measuring signal, which corresponds to the deflection of theoscillating mass in the detection direction; a read-out circuit forreading out and pre-processing the measuring signal. The read-outcircuit includes a demodulator, with which a useful signal and aquadrature signal are extractable from the measuring signal. Theread-out circuit includes, at least for the useful signal, a sigma-deltaA/D converter, via which a bit sequence including the logic values 0 and1 is generatable.

The extracted quadrature signal, since it remains constant or changesslowly, injects a DC voltage offset into the sigma-delta converter,which causes the generation of undesirable sounds, i.e., spectralcomponents at a defined frequency, in the frequency spectrum of thedigital bit stream. The frequency of the sounds is proportional to theDC voltage offset at the input of the analog-digital converter.

At low DC voltage values, these sounds are situated in the signalbandwidth and worsen the signal-to-quantization-noise ratio or “SQNR” ofthe analog-digital converter. In order to suppress the sounds, ditheringis applied: a pseudo-random noise is injected into the analog-digitalconverter in order to interrupt the periodic forms caused by the inputof DC components.

In order to ensure an effective dithering, a sufficient noise power mustbe injected. The quantization noise of the output of the analog-digitalconverter increases as a result. A further disadvantage is that thedithering increases the temporal variation of the output signal of theintegrator of the sigma-delta converter. In a higher-order single bitsigma-delta converter, this means that the stable input range, i.e., themaximum input amplitude at which the analog-digital converter is stable,is reduced.

Moreover, particular attention must be paid when implementing thearrangement of the analog-digital converter in order to reduce theparasitic coupling between particular nodes of the analog-digitalconverter. These couplings may result in a shift of the higher frequencysounds into a lower frequency range, which requires an even higherdithering.

One alternative to dithering is the injection of a D/C voltage offset oran offset voltage, which eliminates the sound or sounds from the signalband. The injection of the D/C voltage offset requires a carefulassessment of the amplitude of the offset. The injection of the D/Cvoltage offset results in an increase in the thermal noise and in a lossof the signal fluctuation (signal swing) or in an increase in thequantization noise, all of which are proportional to the amplitude ofthe offset.

On the one hand, it is important to keep the D/C voltage offset or theoffset voltage low in order to preferably avoid the aforementioneddisadvantages. On the other hand, the offset voltage must besufficiently high in order to eliminate the sounds from the range of thesignal band, at least for a small angle velocity in all operatingconditions, i.e., for an arbitrary value of the quadrature.

U.S. Patent Application Publication No. US 2017/0023364 A1 describes amethod for compensating for a sensitivity of an inertial sensorincluding a resonator and an acceleration sensor. The method includes:adding a test signal to a quadrature tuning voltage, which is applied tothe resonator of the inertial sensor; receiving a quadrature errorsignal from the acceleration sensor of the inertial sensor; detecting aphase difference between the quadrature error signal and the testsignal; and determining a bandwidth of the acceleration sensor based onthe detected phase difference. The bandwidth indicates the sensitivityof the acceleration sensor.

SUMMARY

The present invention provides a rotation rate sensor and a method foroperating a rotation rate sensor.

Preferred refinements are the present invention are disclosed herein.

According to one aspect, the present invention relates to a rotationrate sensor. In accordance with an example embodiment of the presentinvention, the rotation rate sensor include at least: one oscillatingmass, which is deflectable in a drive direction and in a detectiondirection oriented perpendicularly to the drive direction; one drivecircuit for prompting a defined oscillatory movement of the oscillatingmass in the drive direction; one circuit for detecting a measuringsignal, which corresponds to the deflection of the oscillating mass inthe detection direction; one read-out circuit for reading out andpre-processing the measuring signal. The read-out circuit includes ademodulator with which a useful signal and a quadrature signal areextractable from the measuring signal. The read-out circuit includes asigma-delta A/D converter at least for the useful signal, via which abit sequence including the logic values 0 and 1 is generatable. Anoffset voltage is feedable to the sigma-delta A/D converter, which isselected in such a way that tonal artifacts in the frequency spectrum ofthe digitized useful signal, which are caused by a low signal amplitudeand/or a DC voltage component in the useful signal, are shifted into afrequency range outside of the bandwidths of the useful signal to beexpected.

According to an example embodiment of the present invention, a newapproach for the front end of rotation rate sensors is provided, inwhich the amplitude of the DC voltage offset or the offset voltage maybe programmed as a function of the quadrature signal. This is possibleand relatively easy to implement, since the quadrature signal hasalready been read by the demodulator of the read-out circuit of arotation rate sensor.

Alternatively, the programming of the amplitude of the offset voltagemay take place via a manual calibration, since the quadrature signaldoes not change significantly over time, or takes place via an automaticcalibration with each start-up of a rotation rate sensor.

The manual or automatic calibration of the offset voltage as a functionof the amplitude of the quadrature signal enables a lower impact on theperformance of the sigma-delta converter with respect to noise andsignal fluctuations, as compared to the related art.

The present invention is an alternative to dithering for solving theproblem relating to the presence of sounds in vibrating gyroscopes thatinclude sigma-delta converters, as a result of which the above-mentioneddisadvantages of dithering may be preferably avoided.

One possibility is to inject a constant DC voltage offset, regardless ofthe output value of the sigma-delta converter. As a result, the fullscope or the full scale of the analog-digital converter remainsunchanged, as does the quantization noise. In addition, the offsetvoltage generates a low thermal noise, which is proportional to theamount of the offset input. The offset voltage utilizes a portion of thefull scope or the full scale of the analog-digital converter.

In one preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that the offsetvoltage, in particular, the sign of the offset voltage, is selected as afunction of the quadrature signal.

It should be considered that the quadrature signal also generates anoffset. The entire input offset must therefore be considered whencalculating the frequency of the sound. The injected or input offsetvoltage is identified by Voff, and the quadrature is identified byQ_(A). The worst case occurs when Voff and Q_(A) have reversed signs,because a lower input offset brings the sound to a lower frequency. Thismeans that Voff must be dimensioned while taking this case into account,in which Voff and Q_(A) have opposing signs. In this case, the soundmust be situated outside the signal bandwidth.

The input offset voltage must be sufficiently high in order to removethe sound from the signal band. It may be subsequently digitallysubtracted. The use of a higher offset voltage entails somedisadvantages, however: the thermal noise caused by the offset voltageis higher, and if the total input offset (Voff+Q_(A)) is high, thedynamic range available for the input signal decreases, since a portionof the input signal is already occupied by the offset.

Thus, according to an example embodiment of the present invention, itmay be advantageous to trim the sign and the amplitude of the offsetvoltage based on the amplitude and the sign of the quadrature signal. Ina rotation rate sensor, the quadrature signal is already extracted viademodulation from the measuring signal. This enables a compensation ofthe residual quadrature present in the measuring signal, which is causedby a phase shift due to parasites in the circuit. These measured piecesof information may easily be utilized one time at the end of the trialphase or at the start-up in order to digitally trim the offset voltage.

In one further preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that the read-outcircuit includes a calibration module to which the quadrature signal isfeedable, and that the calibration module is designed for the purpose ofdetermining the offset voltage while taking the quadrature signal intoaccount. In this way, it is possible to determine thetemperature-dependent influence on the quadrature signal multiple timesin an “on-chip” manner.

In one further preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that the usefulsignal and the offset voltage are addable together at the input of thesigma-delta A/D converter.

In one further preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that the usefulsignal is reconstructable by the sigma-delta A/D converter on the basisof the generated bit sequence using reference voltages −Vref, +Vref, andthe reconstructed useful signal is subtractable from the analog usefulsignal at the input of the sigma-delta A/D converter. One of the tworeference voltages −Vref, +Vref is acted upon by offset voltage Voff insuch a way that the useful signal is reconstructable using referencevoltages −Vref, −Vref-Voff for the logic value and reference voltages+Vref+Voff, +Vref for logic value 1 of the bit sequence.

As a result, the single bit quantizer includes asymmetrical references.The injection of the offset voltage using a single bit quantizerincluding asymmetrical references is easily implementable.

In one further specific embodiment of the rotation rate sensor accordingto the present invention, it is provided that the sigma-delta A/Dconverter includes a circuit arrangement for reconstructing the usefulsignal, including a differential amplifier (A), which includes anegative voltage input VinN, a positive voltage input VinP, a negativevoltage output VoutN and a positive voltage output VoutP, a firstcapacitance C1, via which positive voltage output VoutP is fed back tonegative voltage input VinN, a second capacitance C2, via which negativevoltage output VoutN is fed back to positive voltage input VinP, a firstresistance Rdac1 and first switches s1, s2, via which first voltage V1is selectively applicable at negative voltage input VinN or at positivevoltage input VinP, and a second resistance Rdac2 and second switchess3, s4, via which a second voltage V2 is selectively applicable atnegative voltage input VinN or at positive voltage input VinP, first andsecond switches (s1, s2, s3, s4) being activatable by the bit sequencegenerated by the sigma-delta A/D converter. The difference between firstvoltage V1 and second voltage V2 corresponds to reference voltage Vref:V1−V2=Vref. First resistance (Rdac1) and second resistance (Rdac2) arevariably adjustable, so that reference voltage Vref is acted upon byoffset voltage Voff.

In one further preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that at least onesub-resistance ΔR1 of first resistance Rdac1 and at least onesub-resistance ΔR2 of second resistance Rdac2 is selectively bridgeablewith the aid of a third switch s5, s6, and that third switches s5, s6are activatable via the bit sequence generated by the sigma-delta A/Dconverter.

In one further preferred specific embodiment of the rotation rate sensoraccording to the present invention, it is provided that a subtractordownstream from the sigma-delta A/D converter is provided in order topurge the digitized useful signal of a signal offset corresponding tothe offset voltage.

According to a second aspect, the present invention relates to a methodfor operating a rotation rate sensor. In accordance with an exampleembodiment of the present invention, the rotation rate sensor includesat least one oscillating mass, which is deflectable in a drive directionand in a detection direction oriented perpendicularly to the drivedirection; a drive circuit for prompting a defined oscillatory movementof the oscillating mass in the drive direction; a circuit for detectinga measuring signal, which corresponds to the deflection of theoscillating mass in the detection direction; a read-out circuit forreading out and pre-processing the measuring signal. The read-outcircuit includes a demodulator, with which a useful signal and aquadrature signal are extracted from the measuring signal. The read-outcircuit includes a sigma-delta A/D converter at least for the usefulsignal, which generates a bit sequence including the logic values 0 and1, an offset voltage being fed to the sigma-delta A/D converter, whichis selected in such a way that tonal artifacts in the frequency spectrumof the digitized useful signal, which are caused by a low signalamplitude and/or a DC voltage component in the useful signal, areshifted into a frequency range outside of the bandwidths of the usefulsignal to be expected.

In one preferred specific embodiment of the method according to thepresent invention, it is provided that the offset voltage and, inparticular, the sign of the offset voltage are determined while takingthe quadrature signal into account.

In one further preferred specific embodiment of the method according tothe present invention, it is provided that the offset voltage isdetermined in an event-controlled manner, in particular, initiated by anactivation of the rotation rate sensor.

In one further preferred specific embodiment of the method according tothe present invention, it is provided that the useful signal and offsetvoltage Voff are added up at the input of the sigma-delta A/D converter.

In one further preferred specific embodiment of the method according tothe present invention, it is provided that the sigma-delta A/D converterreconstructs the useful signal on the basis of the generated bitsequence using reference voltages −Vref, +Vref, and subtracts thereconstructed useful signal from the analog useful signal at the inputof the sigma-delta A/D converter, one of the two reference voltages−Vref, +Vref being acted upon by offset voltage Voff in such a way thatthe useful signal is reconstructed using reference voltages −Vref,−Vref-Voff for logic value 0 and reference voltages +Vref+Voff, +Vreffor logic value 1 of the bit sequence.

In one further preferred specific embodiment of the method according tothe present invention, it is provided that the digitized useful signalis purged of a signal offset corresponding to the offset voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in greater detail below withreference to exemplary embodiments schematically indicated in thefigures.

FIG. 1 shows a schematically represented specific embodiment of therotation rate sensor according to the present invention.

FIG. 2 shows a schematically represented sigma-delta converter of afurther specific embodiment of the rotation rate sensor according to thepresent invention, including a single bit quantizer having asymmetricalreferences.

FIG. 3 shows the property of the single bit quantizer of the sigma-deltaconverter of the specific embodiment of the rotation rate sensoraccording to the present invention according to FIG. 2 .

FIG. 4 shows an implementation example of the sigma-delta converter ofthe specific embodiment of the system according to the present inventionaccording to FIG. 2 for an integrator.

FIG. 5 shows a schematically represented flowchart of one specificembodiment of the method according to the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the figures, identical reference numerals refer to identical orfunctionally identical elements.

One specific embodiment of the rotation rate sensor according to thepresent invention, or circuit arrangement 100 of a rotation rate sensorrelevant to the invention is schematically represented in FIG. 1 .

The rotation rate sensor includes a preferably micromechanical sensorelement including an oscillating mass, which is deflectable in a drivedirection and in a detection direction oriented perpendicularly to thedrive direction. The oscillating mass prompts a defined oscillatorymovement in the drive direction, specifically at a resonance frequencyf0.

In the case of a rotational movement of the rotation rate sensor about arotational axis, which is oriented perpendicularly to the drivedirection and perpendicularly to the detection direction, theoscillating mass is acted upon by a Coriolis force. This Coriolis forceeffectuates a deflection of the oscillating mass in the detectiondirection, which is capacitively detected here. In FIG. 1 , arepresentation of the sensor element including the oscillating mass andthe drive circuit has been dispensed with. Only a measuring capacitance2 is represented, with which the Coriolis force acting upon theoscillating mass in the detection direction is detected. With the aid ofa downstream capacitance voltage C/V converter 4, this capacitive signalis converted into a voltage signal, which is referred to below as ameasuring signal. In the rotation rate sensor described herein,measuring capacitance 2 and C/V converter 4 form the main components ofcircuit 10 for detecting the measuring signal.

The measuring signal includes essentially two signal components.

One of the two signal components is generated by the Coriolis force. Itsamplitude is proportional to the angle velocity. This useful signal istherefore also referred to as rate R.

The other signal component is caused by manufacturing-related deviationsfrom an ideal sensor geometry and sensor structure such as, for example,from mechanical misalignments between the moved oscillating mass and theelectrodes for detecting measuring signals. This signal component is inphase with the position of the oscillating mass and is referred to asquadrature signal Q. It is phase shifted by 90 degrees relative touseful signal R.

The measuring signal may thus be described as follows:

${{R(t)} + {Q(t)}} = {{{\Omega(t)}*{\sin\left( {2\pi f_{0}t} \right)}} + {Q_{A}*{\sin\left( {{2\pi f_{0}t} + \frac{\pi}{2}} \right)}}}$

Ω(t) is the angle velocity and Q_(A) is the amplitude of the quadraturesignal.

A read-out circuit for reading out and pre-processing the measuringsignal is situated downstream from circuit 10 for detecting themeasuring signal. Here, useful signal R and quadrature signal Q areextracted from the measuring signal with the aid of demodulators 6, inorder to then initially be analogically/digitally converted in separatesignal paths and then to be digitally further processed or evaluated.

Since quadrature signal Q and the drive signal for the oscillating massof the sensor are in phase, a clock signal 14 obtained from the drivesignal is used for the demodulation of quadrature signal Q.

Clock signal 12 used for the demodulation of useful signal R is alsoobtained from the drive signal, specifically, via phase shifting by 90degrees. Clock signal 12 is therefore in phase with R(t) and has afrequency f0.

The two signals R(t) and Q(t) frequently experience a phase shift ϕ_(d)with respect to the demodulation clock due to parasitic effects in thecircuit: according to the present invention, the demodulation takesplace before the analog-digital conversion. If the

${R(t)} = {{Q(t)} = {{{\Omega(t)}*{\sin\left( {{2\pi f_{0}t} + \phi_{d}} \right)}} + {Q_{A}*{\sin\left( {{2\pi f_{0}t} + \frac{\pi}{2} + \phi_{d}} \right)}}}}$phase shift ϕ_(d) is equal to 0, the demodulation of quadraturesignature Q(t) delivers spectral components at multiples of 2*f0, whichmay be easily filtered out, whereas the demodulation of useful signalR(t) delivers angle velocity Ω(t) in the base band.

If phase shift ϕ_(d) is not equal to 0, the demodulation of thequadrature signature generates a DC voltage component or DC component inthe useful signal. This proves problematical, in particular, for asigma-delta A/D conversion, since a DC voltage component in this casecauses sounds in the signal spectrum of the digitized useful signal,which for sufficiently small values of Q_(A) are situated in the signalbandwidth of angle velocity Ω(t), and thus result in a reduction of thequantization noise ratio (SQNR) of the sigma-delta analog-digitalconverter.

In the specific embodiment shown in FIG. 1 , both a sigma-delta A/Dconverter 8 is provided in the signal path of quadrature signal Q and asigma-delta A/D converter 24 including an integrator 23, a backend-ADC22, and a quantizer 20 are provided in the signal path of useful signalR.

According to the present invention, an offset voltage V_(off) is fed tosigma-delta A/D converter 24, which is selected in such a way that tonalartifacts in the frequency spectrum of the digitized useful signal,which are caused by a low signal amplitude and/or a DC voltage componentin the useful signal, are shifted into a frequency range outside of thebandwidths of the useful signal to be expected, i.e., of the anglevelocity at to be detected.

In principle, offset voltage V_(off) could be determined once, forexample, in a trim process by the manufacturer, and then be utilizedunchanged and separately from the individually determined quadraturesignature for acting upon the sigma-delta A/D converter.

In the exemplary embodiment described herein, however, offset voltageV_(off) is selected as a function of quadrature signal Q. For thispurpose, quadrature signal Q is fed to a calibration module 16, which inthis case is part of the read-out circuit. On the basis of quadraturesignal Q, calibration module 16 determines, in particular, the sign ofoffset voltage V_(off), but may also determine the magnitude of offsetvoltage V_(off).

In a first variant of the present invention, offset voltage V_(off) issimply added to useful signal R at the input of sigma-delta A/Dconverter 24 in order to compensate for a DC voltage component in usefulsignal R.

In a further, particularly advantageous variant of the presentinvention, offset voltage V_(off) is injected into sigma-delta A/Dconverter 24, which is explained in greater detail in connection withFIG. 2 .

According to FIG. 2 , sigma-delta A/D converter 24 reconstructs theuseful signal with the aid of a D/A converter DAC 21, specifically, onthe basis of the generated bit sequence and using reference voltages−V_(ref) and +V_(ref) in order to then subtract the reconstructed usefulsignal from the analog useful signal at the input of the sigma-delta A/Dconverter. Offset voltage V_(off) is injected here into sigma-delta A/Dconverter 24 by one of the two reference voltages −V_(ref) or +V_(ref)being acted upon by offset voltage V_(off) in such a way that the usefulsignal is reconstructable using reference voltages −V_(ref) or−V_(ref)−V_(off) for logic value 0 and reference voltages+V_(ref)+V_(off) or +V_(ref) for logic value 1 of the bit sequence. Thisis illustrated by FIG. 3 . X-axis 32 symbolizes the input of single-bitquantizer 20, whereas y-axis 34 indicates the corresponding value of thereference voltage for D/A converter DAC 21. If the output of quantizer20 is positive, i.e., 1, the output value is +Vref+ΔV or +Vref+Voff, ifthe output is 0, the output value is −Vref. Single bit quantizer 20 thusincludes asymmetrical references.

This corresponds to a single bit quantizer having an offset +ΔV/2, thefull scale of the single bit quantizer being expanded from +/−Vref to+/−Vref+ΔV/2.

The DC voltage component of the useful signal is, virtually 7,compensated for with the aid of the useful signal reconstructed by D/Aconverter DAC 21. Offset voltage V_(off) is injected here namely by thefeedback loop of sigma-delta A/D converter 24 being designed to followthe input signal of sigma-delta A/D converter 24. For this reason, anoffset of opposite polarity is generated by using more negative thanpositive references. This is directly reflected in the generated bitsequence, which will consequently include more zeros than ones.

FIG. 4 represents an implementation example of sigma-delta converter 24shown in FIG. 2 including two different reference voltages for an analogtime integrator. The sigma-delta A/D converter includes a circuitarrangement for reconstructing the useful signal, which includes: adifferential amplifier A, which includes a negative voltage input VinN,a positive voltage input VinP, a negative voltage output VoutN and apositive voltage output VoutP, a first capacitance C1, via whichpositive voltage output VoutP is fed back to negative voltage inputVinN, a second capacitance C2, via which negative voltage output VoutNis fed back to positive voltage input VinP, a first resistance Rdac1 andfirst switch s1, s2, via which a first voltage V1 is selectivelyapplicable at negative voltage input VinN or at positive voltage inputVinP, and a second resistance Rdac2 and second switches s3, s4, viawhich a second voltage V2 is selectively applicable at negative voltageinput VinN or at positive voltage input VinP. First and second switchess1, s2, s3, s4 are activatable via the bit sequence generated by thesigma-delta A/D converter. The difference between first voltage V1 andsecond voltage V2 corresponds to reference voltage Vref: V1−V2=Vref.First resistance Rdac1 and second resistance Rdac2 are variablyadjustable so that reference voltage Vref is acted upon by offsetvoltage Voff. A sub-resistance ΔR1 of first resistance Rdac1 and asub-resistance ΔR2 of second resistance Rdac2 are selectively bridgeablewith the aid of a third switch s5, s6, and third switches s5, s6 areactivatable via the bit sequence generated by the sigma-delta A/Dconverter, specifically, by “D” or “NOT(D)”. Switches s1, s4 areactivatable via the bit sequence generated by the sigma-delta A/Dconverters, specifically, by “D”, whereas switches s2, s3 areactivatable by “NOT(D)”. Alternatively, switches s1, s4 are activatableby the bit sequence generated by the sigma-delta A/D converter,specifically, by “NOT(D)”, whereas switches s2, s3 are activatable by“D”.

According to the present invention, the circuit arrangement is easy toimplement and has only minimal effects on the overall circuit area.

The specific embodiment of the method according to the present inventionrepresented in FIG. 5 includes three steps. In step S1, a measuringsignal, which corresponds to the deflection of an oscillating mass ofthe rotation rate sensor in the detection direction, is detected by acircuit of a rotation rate sensor. In step S2, the measuring signal isread out by a read-out circuit of the rotation rate sensor andpre-processed, the read-out circuit including a demodulator, with whicha useful signal and a quadrature signal are extractable from themeasuring signal, and the read-out circuit including, at least for theuseful signal, a sigma-delta A/D converter, via which a bit sequenceincluding logic values 0 and 1 is generatable. In step S3, an offsetvoltage Voff is fed to the sigma-delta A/D converter, which is selectedin such a way that tonal artifacts in the frequency spectrum of thedigitized useful signal, which are caused by a low signal amplitudeand/or a DC voltage component in the useful signal, are shifted into afrequency range outside of the bandwidths of the useful signal to beexpected.

The present invention, although it has been fully described above withreference to preferred exemplary embodiments, is not restricted thereto,but is modifiable in a variety of ways.

What is claimed is:
 1. A rotation rate sensor, comprising: anoscillating mass which is deflectable in a drive direction and in adetection direction oriented perpendicularly to the drive direction; adrive circuit configured to prompt a defined oscillatory movement of theoscillating mass in the drive direction; a circuit configured to detecta measuring signal which corresponds to the deflection of theoscillating mass in the detection direction; a read-out circuitconfigured to read out and pre-process the measuring signal, theread-out circuit including at least one demodulator, with which a usefulsignal and a quadrature signal are extractable from the measuringsignal, and the read-out circuit including, at least for the usefulsignal, a sigma-delta A/D converter, via which a bit sequence includinglogic values 0 and 1 is generatable thereby digitizing at least theuseful signal; wherein an offset voltage is feedable to the sigma-deltaA/D converter, which is selected in such a way that tonal artifacts in afrequency spectrum of the digitized useful signal, which are caused by alow signal amplitude and/or a DC voltage component in the useful signal,are shifted into a frequency range outside of bandwidths of the usefulsignal to be expected.
 2. The rotation rate sensor as recited in claim1, wherein a sign of the offset voltage is selected as a function of thequadrature signal.
 3. The rotation rate sensor as recited in claim 2,wherein the read-out module includes a calibration module, to which thequadrature signal is feedable, and the calibration module is configuredto determine the offset voltage while taking the quadrature signal intoaccount.
 4. The rotation rate sensor as recited in claim 1, wherein theuseful signal and the offset voltage are added together at an input ofthe sigma-delta A/D converter.
 5. The rotation rate sensor as recited inclaim 1, wherein the useful signal is reconstructable via thesigma-delta A/D converter based on the generated bit sequence usingreference voltages, and the reconstructed useful signal is subtractedfrom the analog useful signal at an input of the sigma-delta A/Dconverter, wherein one of the reference voltages is acted upon by theoffset voltage in such a way that the useful signal is reconstructableusing the reference voltages for the logic value 0 and the referencevoltages for the logic value 1 of the bit sequence.
 6. The rotation ratesensor as recited in claim 5, wherein the sigma-delta A/D converterincludes a circuit arrangement for reconstructing the useful signal,including: differential amplifier, which includes a negative voltageinput, a positive voltage input, a negative voltage output and apositive voltage output; a first capacitance, via which the positivevoltage output is fed back to the negative voltage input; a secondcapacitance, via which the negative voltage output is fed back to thepositive voltage input; a first resistance and first switches, via whicha first voltage is selectively applicable at the negative voltage inputor at the positive voltage input; and a second resistance and secondswitches, via which a second voltage is selectively applicable at thenegative voltage input or at the positive voltage input; wherein thefirst and second switches are activatable via the bit sequence generatedby the sigma-delta A/D converter, a difference between the first voltageand the second voltage corresponds to the reference voltage, and thefirst resistance and the second resistance are variably adjustable insuch a way that the reference voltage is acted upon by the offsetvoltage.
 7. The rotation rate sensor as recited in claim 6, wherein atleast one sub-resistance of the first resistance and at least onesub-resistance of the second resistance are selectively bridgeable usinga third switch, and the third switches are activatable by the bitsequence generated by the sigma-delta A/D converter.
 8. The rotationrate sensor as recited in claim 1, further comprising: a subtractordownstream from the sigma-delta A/D converter configured to purge thedigitized useful signal of a signal offset corresponding to the offsetvoltage.
 9. A method for operating a rotation rate sensor including anoscillating mass, which is deflectable in a drive direction and in adetection direction oriented perpendicularly to the drive direction, adrive circuit configured to prompt a defined oscillatory movement of theoscillating mass in the drive direction, a circuit configured to detecta measuring signal, which corresponds to the deflection of theoscillating mass in the detection direction, and a read-out circuitconfigured to read out and pre-process the measuring signal, theread-out circuit including a demodulator, with which a useful signal anda quadrature signal are extracted from the measuring signal, and theread-out circuit including, at least for the useful signal, asigma-delta A/D converter, which generates a bit sequence includinglogic values 0 and 1 thereby digitizing at least the useful signal, themethod comprising: feeding an offset voltage to the sigma-delta A/Dconverter, which is selected in such a way that tonal artifacts in afrequency spectrum of the digitized useful signal, which are caused by alow signal amplitude and/or a DC voltage component in the useful signal,are shifted into a frequency range outside of bandwidths of the usefulsignal to be expected.
 10. The method as recited in claim 9, wherein asign of the offset voltage are determined while taking the quadraturesignal into account.
 11. The method as recited in claim 10, wherein theoffset voltage is determined in an event-controlled manner, initiated byan activation of the rotation rate sensor.
 12. The method as recited inclaim 9, wherein the useful signal and the offset voltage are addedtogether at an input of the sigma-delta A/D converter.
 13. The method asrecited in claim 9, wherein the sigma-delta A/D converter reconstructsthe useful signal based on the generated bit sequence using referencevoltages and subtracts the reconstructed useful signal from the analoguseful signal at an input of the sigma-delta A/D converter, one of thereference voltages being acted upon by the offset voltage in such a waythat the useful signal is reconstructed using the reference voltages forthe logic value 0 and reference voltages for the logic value 1 of thebit sequence.
 14. The method as recited in claim 9, wherein thedigitized useful signal is purged of a signal offset corresponding tothe offset voltage.